Support arm



FIG. 1 is a front view of a support arm

FIG. 2 is a right side view of a support arm

FIG. 3 is a top view of a support arm; and,

FIG. 4 is a bottom view of a support arm.

The broken line showing of a support arm stake is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a support arm, as shown. 